Thursday, January 27, 2011

Chemistry for Kids, Part 2: Acids and Bases

 Lesson 2/Week 2: Acids and Bases

"Matter, the stuff around us, is used to create atoms. Atoms are used to create the elements. Elements are used to create molecules. It just goes on. Everything you see is built by using something else."  Source:

Molecules- Show pics at this link and explain what each is/does:

Water Molecule is made up of 2H's and 1O (draw on whiteboard)
Demonstrate in drawing how acids and bases "take" from water: H goes to acid/OH goes to base.
Split water molecule in drawing on white board. Compare split to a matching game: if you were to play matching with a split-up water molecule, the match would be OH-H, not OH-OH or H-H.

Acids & Bases
Common acids: Fruit juice, battery acid, vinegar (pH 4), lemon juice, shampoos
Acids taste sour & Acids are corrosive (they eat away at things)
 ex. soda will dissolve a nail or a coin over time bc of the citric acid in it
Acids lose their acidity when mixed with bases

Common bases: bleach, soap, hair conditioner, drain cleaner, baking soda (pH 8)
Bases are slippery and taste bitter
Bases lose their basicity when mixed with acids

Strong acids and strong bases can be dangerous- never touch, taste, swallow, or smell them because they can burn you or make you sick!!

Why they interact with each other and weaker acids/bases: They share/swap OH's & H's until each one is "happy" or neutral. Show pH scale how neutral is in the middle.
Activity: Use M&M's and ask them to swap in groups of 2 until everyone is happy with the amount they have.

  • Scientists use the pH (parts Hydrogen) scale to tell if an acid or base is weak or strong. Water is neutral.
  • "Knowing whether something is acidic or basic can be very useful. For example, wasp stings are alkaline but bee stings are acidic. So if you get stung you need to put bicarbonate of soda on a bee sting and vinegar on a wasp sting. Hair conditioner is slightly alkaline as shampoo tends to be slightly acidic, so any traces of shampoo can be neutralised by the conditioner." 

Knowing what we now know about acids and bases, we're going to do a series of experiments to help us try and guess whether something is an acid or base and/or see how they react/what they do.

Pre-make the following 7 solutions for use in the Experiments below:
2qts Water + 2 cups baking soda 1qt Water + 1 cup sugar 1qt Water + 1/2 cup salt
1qt Water + 1/4 cup citric acid 1qt Vinegar 1/2 qt lemon juice
Red Cabbage Solution*

* Add chopped Red Cabbage to boiling water, allow to simmer until water is a deep purple, then allow to cool, separate the cabbage leaves from the water using a colander, refrigerate when not in use.

Experiment: Have some fizzy fun! adding several of our proven acids (lemon juice, citric acid solution, vinegar) to some baking soda and seeing if a stronger acid reacts more strongly. The kids then checked some of our bases (soap, baking soda, borax) to see if anything happened (nope) and the neutrals (water, sugar water, salt water) as well (ditto).

Experiment: Does an acid or base clean pennies better?
Split into groups of 2, give each group 6 dixie cups, 6 dirty pennies.
Cleaning solutions we're using: lemon juice, vinegar, citric acid solution, soapy water, baking soda water, borax water) Drop a penny into each cup of cleaning solution and wait a few minutes before examining the penny to see if it's shiny.

Experiment: Let's see if we're right!
 Red cabbage water is an indicator of pH. Although it can't be used to determine exact pH, it can distinguish between acid (pH of 0 to 6), neutral (pH near 7), and base (pH of 8 to 14).

acid                     neutral                       base

0   1   2   3   4   5   6   7   8   9   10  11  12  13  14
In this activity:
  • If the indicator turns the solution red or pink, the solution is an acid.
  • A purple solution indicates that it is neutral, neither an acid nor a base.
  • If the indicator turns the solution blue or green, the solution is a base.

Activity: Invisible Ink Writing.
You can even use the power of acid and base chemistry to write secret messages! You can write a message in invisible ink by doing this: Dip a Q-tip in baking soda solution and write a message on white paper- careful not to use too much liquid! Once the paper dries, rub a red grape over the message OR spray the message with a spray bottle filled with Red Cabbage Indicator. Handy hint: using a hair dryer speeds things up.

Activity: Magic Liquids
Materials: 1 cup water, 1 cup baking soda solution (above), 1 cup water + vinegar, Red Cabbage Indicator, 3 glasses/clear cups
-Fill each of the three cups with one of the first three liquids above.
-Take turns adding the Red Cabbage Indicator to each, ask children to predict what color each will turn.

Activity: Blow up a balloon using baking soda and vinegar.
Pour vinegar into a bottle with a narrow neck (soda or water bottle, cleaned out, no label) until it is about 1/4 of the way full. Use a funnel to put a small amount of baking soda in a deflated balloon. Place lip of balloon over rim of bottle and shake the baking soda out, then watch it inflate. Explain that the reaction between the acidic vinegar and the basic baking soda gives off gas that causes the balloon to inflate.

No comments:

Post a Comment

Do you have a comment, question or suggestion to share?